<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      .container {
        position: relative;
      }
      .mc1,
      .mc2,
      .mc3 {
        width: 300px;
        height: 240px;
        position: absolute;
      }
      .mc1 {
        background-color: red;
        z-index: 100;
      }
      .mc2 {
        background-color: green;
        left: 30px;
        top: 30px;
        z-index: 10;
      }
      .mc3 {
        background-color: blue;
        left: 60px;
        top: 60px;
        z-index: 0;
      }
    </style>
  </head>
  <body>
    <!-- z-index: 默认值是0 -->
    <div class="container">
      <div class="mc1"></div>
      <div class="mc2"></div>
      <div class="mc3"></div>
    </div>
  </body>
</html>

<!-- Shift + Alt + 上下 -->
